These finely crafted measuring devices areused for gaging V, American National orU.S. standard 60° threads Gages are notched for measuring inside threadsof small holes and nuts as well as externalthreads Set of 51 screw pitches combines all sizes from4 to 84, including 11-1/2 and 27 pipe threadsizes Knurled thumb nuts lock the case in an open orclosed position